The Effects of Carbonated Water Upon Gastric and Cardiac Activities and Fullness in Healthy Young Women

J Nutr Sci Vitaminol, 58, 333–338, 2012

The Effects of Carbonated Water upon Gastric and Cardiac Activities and Fullness in Healthy Young Women

Shiori WAKISAKA1,4, Hajime NAGAI2, Emi MURA2, Takehiro MATSUMOTO3, Toshio MORITANI4 and Narumi NAGAI1,*

1 Graduate School of Human Science and Environment, University of Hyogo, 1–1–12 Shinzaike-honcho, Himeji, Hyogo 670–0092, Japan 2 Frontier Center for Value Creation, Suntory Business Expert Limited, 57 Imaikami-cho, Nakahara-ku, Kawasaki, Kanagawa 211–0067, Japan 3 Institute for Water Science, Suntory Business Expert Limited, 5–2–5 Yamazaki, Shimamoto-cho, Mishima-gun, Osaka 618–0001, Japan 4 Graduate School of Human and Environmental Studies, Kyoto University, Sakyo-ku, Kyoto 606–8501, Japan (Received February 27, 2012)

Summary Although previous reports suggested that carbonated water drinking was effective against gastrointestinal symptoms, there is little information about the effects of carbonated water on gastric and appetite sensation. We therefore investigated the effect of carbonated water on short-term fullness with respect to gastric and cardiac responses in 19 healthy young women. Each subject was tested on three separate days at approximately 9 a.m. after an overnight fast. Gastric motility, evaluated by electrogastrography (EGG) and heart rate (HR), was measured for 20 min in the fasting state and 40 min after ingestion of water. Preloads consisted of an equivalent amount (250 mL) of water (W) or carbonated water (CW) and no drinking (blank). Fullness scores were measured using visual analog scales. To determine gastric motility, we assessed the component of bradygastria (1–2 cycles/ min [cpm]), normogastria (2–4 cpm), tachygastria (4–9 cpm), and dominant frequency of the EGG power spectrum. After ingestion of CW, signifi cant increases in fullness scores were observed compared with W. All postprandial EGG powers were signifi cantly greater than preprandial, but no group difference was found. However, a dominant frequency tended to shift toward a lower band after ingestion of W. A signifi cantly higher HR was found following consumption of CW as opposed to W. Multiple regression analysis revealed that increased HR was a signifi cant variable contributing to the variances in fullness after ingestion of CW at 40 min. Our data suggest that CW may induce a short-term, but signifi cant, satiating effect through enhanced postprandial gastric and cardiac activities due possibly to the increased sympathetic activity and/or withdrawal of parasympathetic activity. Key Words carbonated water, fullness, gastric motility, electrocardiography, heart rate

Carbonated water is plain water or mineral water into water may useful for prevention of overeating. which carbon dioxide gas has been added under pres- The mechanical motility of the stomach is regulated sure. In Japan, the consumption of carbonated water by gastric electrical activity, which consists of rhyth- has been gradually increased due to a health conscious mic slow waves (i.e., normal wave) at a frequency of 3 trend (1). According to previous studies (2, 3), car- cycles/min (cpm) delivered from pacemaker cells (5, 9). bonated water intake had therapeutic effects including Electrogastrography (EGG) has gained popularity with relieving gastrointestinal symptoms such as dyspepsia broad applications as a functional indicator of gastric through improved gastric motility. Since carbonated motility because it is an accessible and noninvasive water is an effervescent beverage, carbonated water method in which a cutaneous recording of gastric elec- brings a perception of gastric fullness through gastric trical activity is made from surface electrodes placed on distention (4), which is also associated with gastric the abdomen (9). The parameters calculated from EGG motility (5). We recently reported that appetite sensa- power spectral analysis, such as EGG powers (brady- tions were positively correlated with the intensity of gas- gastria, 1–2 cpm; normogastria, 2–4 cpm; tachygastria, tric motility (6) evaluated by electrogastrography (EGG) 4–9 cpm) and dominant frequency, have been reported as shown in other studies (7, 8). We therefore hypothe- to be associated with gastric motility (10–12). In addi- sized that carbonated water possesses a satiating effect tion, the changes in EGG powers before or after ingestion through enhancement and/or alteration of gastric of water or a meal (13) as well as intra-individual varia- motility. If this hypothesis is correct, then carbonated tions are taken to refl ect gastric motility. The therapeutic effects of carbonated water on gastric symptoms such * To whom correspondence should be addressed. as dyspepsia have been well studied (14); however, the E-mail: [email protected] satiating effects of carbonated water ingestion and its

333 334 WAKISAKA S et al. association with EGG parameters are less understood. tea, spicy foods, and high-fat foods was prohibited. Interestingly, Chen et al. (5) reported a marked increase Dietary intake was estimated from food records with in cardiac vagal activity after ingestion of 500 mL of photographs taken using a camera-equipped cellular water; however, such an autonomic response following phone for 2 typical weekdays. These records were care- carbonated water ingestion is not known. fully checked by registered dieticians through an inter- Accordingly, the aim of this study was to determine view with each subject on the test day. Energy intake the effect of carbonated water on short-term appetite and nutritional values were calculated using comput- sensations (fullness) and its association with gastric er-assisted procedures (Excel Eiyokun ver. 5.5, Kenpa- motility and cardiac responses in healthy young women. kusya Co., Tokyo, Japan) based on the Japanese food consumption table. MATERIALS AND METHODS Each subject was tested on 3 separate days in a ran- Subjects. We studied 19 healthy young female vol- domized order at approximately 9 a.m. after an over- unteers (18–24 y) recruited from our university student night fast of at least 10 h. After measurements of body population. All subjects were non-smokers, free of any mass and percentage of body fat determined with a symptoms or medical history of gastrointestinal, car- bioelectrical impedance analyzer (InBody520, Biospace diovascular, or other diseases that could affect gastric Co., Soul, Korea), subjects were prepared for an EGG and motility and appetite, and had a habit of eating break- electrocardiogram (ECG), and then, they rested for at fast almost every day. The subject characteristics are least 15 min in a sitting-up position on a bed. After the presented in Table 1. The study protocol was reviewed rest period, ECG and EGG were continuously recorded and approved by the Ethics Committee of the University for 20 min in the preprandial period and 40 min after of Hyogo and was in accordance with the principles of ingestion in a sitting-up, 45˚ inclined position. Fullness the Declaration of Helsinki. All subjects provided writ- scores were measured 3 times, preprandially (Ϫ20 min), ten informed consent. immediately after ingestion, and 40 min after ingestion, Experimental procedures. We conducted a random- using visual analog scales (15). Water and carbonated ized cross-over design experiment with three conditions: water were gradually consumed over a 4 to 5-min period drinking 250 mL of water (W), drinking 250 mL of car- to avoid immediate belching (4). The room temperature bonated water (CW) and no drinking (blank, B). The car- was kept controlled at 25–26˚C, quiet and comfortable, bonated water was made by adding carbon dioxide gas with minimization of arousal stimuli. All subjects were to mineral water used for this study. Both water samples separated by partition screens and requested to main- were categorized as soft water. Mineral contents and CO2 tain their position for the duration of data collection. pressure in representative water samples are presented EGG measurements and spectral analysis procedures. To in Table 2. The temperature of the samples was kept at derive bipolar EGG signals, 2 active electrodes and 1 15˚C just before drinking. ground were positioned on the abdomen according to Subjects were requested to maintain their usual life- the American Motility Society Clinical GI Motility Test- style and body weight for at least 1 wk before the test. ing Task Force (10). The high-cut frequency of the EGG On the day before the test, the consumption of coffee, amplifi er was 0.3 Hz, and the low-cut frequency was 0.016 Hz. This band-pass fi ltering completely eliminated Table 1. Subject characteristics. the electrocardiogram (ECG) and 60 Hz power source artifacts. The EGG signals were amplifi ed (EGG Ampli- nϭ19 fi er BBA-8321, Bio-tex, Kyoto, Japan) and digitized via a 13-bit analog-to-digital converter (DAQ AD135, Elan Age (y) 19.4Ϯ0.4 (18–24) Digital Systems Ltd, Fareham, UK) at a sampling rate of Height (cm) 159.7Ϯ1.4 (152.0–171.0) 0.5 Hz. The acquired data were stored sequentially on a Body mass (kg) 49.9Ϯ1.4 (41.3–63.0) hard disk for later analysis. The root mean square value 2 Body mass index (kg/m ) 19.7Ϯ0.5 (16.1–24.8) of the EGG was calculated as representing the average % Body fat 25.3Ϯ0.7 (20.6–30.2) amplitude. After passing through a Hamming-type data Ϯ Systolic blood pressure 98 2 (122–77) window, power spectral analysis was performed with a (mmHg) fast Fourier transformation on a consecutive 512 time Diastolic blood pressure 65Ϯ2 (84–55) (mmHg) series of data obtained during the test. Signal acquisi- Energy intake (MJ/d) 7.2Ϯ0.3 (4.1–9.2) tion, storage, and processing were performed on a per- sonal computer. The computer programs for sampling MeanϮstandard error (range). and analysis were written in HTBasic (Trans Era ver 9.0,

Table 2. Mineral contents and CO2 pressure in samples.

Sodium Calcium Magnesium Potassium Hardness CO -pressure Sample 2 (mg/100 mL) (mg/100 mL) (mg/100 mL) (mg/100 mL) (mg/L) (kgf/cm2)

Water 1.07 2.98 0.47 0.13 94 0 Carbonated water 1.07 2.98 0.47 0.13 94 3.25 Gastric and Cardiac Activities and Fullness after Carbonated Water 335

(mm) A (mV) Time effect p < 0.001 .3 100 Sample effect p = 0.001 Sample×Time p = 0.005 0 80 B † W *** – .3 CW 2 Dominant Frequency (mV /cpm) 60 † B .0050 *** *** Bradygastria (black) 1 – 2 cpm 40 Normogastria (stripe) 2 – 4 cpm .0025 Tachygastria (white) 4 – 9 cpm 20 Fullness score POWER 0 0 0 24 6 810(cpm) -200 40 (min) FREQUENCY Time Fig. 2. Changes in the fullness score during pre- Fig. 1. A typical set of EGG power spectrum analysis and postprandial periods. The data are expressed as results: raw gastric myoelectrical signal (A) and the meansϮstandard errors. B, blank; W, water; CW, ↓ corresponding power spectrum (B). Dominant carbonated water. Time effect, sample effect, and frequency, a peak of spectrum. sampleϫtime were calculated by repeated ANOVA, which was performed to assess the effect of the two † Utah, USA). experiments (W and CW). pϽ0.05, CWCW–B vs. WW–B To determine the gastric motility, the spectral powers (Kruskal-Wallis test). *** pϽ0.001, vs. PRE (Ϫ20 min) were calculated for the following respective frequency (Dunnett’s multiple comparison test). band and corresponding gastric wave: bradygastria (1–2 cpm), normogastria (2–4 cpm, normal wave), after ingestion of carbonated water than water (sample tachygastria (4–9 cpm) and dominant frequency of EGG effect pϭ0.001, sampleϫtime pϭ0.005. CW: pϽ0.001, power spectrum (6, 10, 16, 17). A dominant frequency, at 40 min, vs. PRE). Focusing on the difference between a peak of the spectrum within the range of 1.0–9.0 cpm, each ingestion and blank, fullness scores after inges- was also calculated (6, 10, 16, 17) (Fig. 1). tion of carbonated water (CWCW–B) were signifi cantly Fullness questionnaires. Visual analog scales (VAS) higher compared to the water (WW–B) at 0 min (CWCW–B: (15, 18), 100 mm in length and anchored at each end, 54Ϯ6 mm, vs. WW–B: 34Ϯ6 mm, pϽ0.05) and 40 min expressing the most positive (extremely) and the most (CWCW–B: 28Ϯ6 mm, vs. WW–B: 12Ϯ4 mm, pϽ0.05). negative rating (not at all), were used to assess fullness EGG parameters sensations. To avoid referring to their previous ratings, Figure 3 shows the time course changes in EGG param- the questionnaires were printed as small booklets show- eters among the 3 trials (water, carbonated water, and ing 1 question at a time (15, 18). blank). After both ingestions, all EGG powers, namely Statistical analyses. All data are expressed as meansϮ bradygastria, normogastria and tachygastria, were sig- standard errors. All analyses were performed using nifi cantly greater compared to before ingestion, but no PASW Statistics 19 for Windows (IBM Inc, Tokyo, group difference was found. As to dominant frequency, Japan). Two-way analysis of variance (ANOVA) with signifi cant decrease was found for 0–20 min after inges- repeated measurements was conducted to assess the tion of water (pϽ0.05); by contrast, such a change was signifi cant effect of carbonated water (CW) vs. the con- not noted after ingestion of carbonated water. trol trial (W) in fullness, heart rate and EGG parameters. Heart rate Additionally, an unpaired t-test or Kruskal-Wallis test Figure 4 shows time courses of pre- and postprandial was used to compare values between CWCW–B and WW–B. heart rate presented at 1 min intervals until 15 min after Signifi cant changes between preprandial (PRE) vs. post- ingestion. Time courses of heart rate differed among the prandial (POST) values in each trial (W, CW, and B) were 2 trials (sample effect pϭ0.040, sample ϫtime pϽ0.001). identifi ed by performing Dunnett’s test (19). Pearson’s With regard to carbonated water ingestion, heart rate correlation analysis was performed to test for associ- was transiently but remarkably increased until the fi rst ations between fullness score and heart rate. Multiple 4 min (pϽ0.001, until 3 min after; pϽ0.05, until 4 min regression analysis was used to evaluate the impact of after, vs. PRE). Conversely, the postprandial values of ⌬heart rate, bradygastria ratio (POST/PRE), and domi- heart rate were gradually decreased after ingestion of nant frequency on fullness scores. The threshold for sig- water and remained signifi cantly lower after 15 min nifi cance was pϽ0.05. (pϽ0.001, vs. PRE). Focusing on the difference between each ingestion and blank, heart rates after ingestion of RESULTS carbonated water (CWCW–B) were signifi cantly higher Fullness compared to the water (WW–B) for the fi rst 5 min, and at Figure 2 shows the time course changes in fullness 7 min and 13 min (pϽ0.05, respectively). among the 3 trials (water, carbonated water, and blank). Correlation analysis and multiple regression analysis Both water and carbonated water raised postprandial The fullness scores and increase in heart rate were fullness; however, higher fullness scores were observed positively correlated at 40 min after ingestion of car- 336 WAKISAKA S et al.

(mV2) (mV2) 1.2 Time effect p < 0.001 1.2 Sample effect p = 0.344 1.0 Sample ×Time p = 0.332 1.0 *** B 0.8 W ** 0.8 *** CW ** 0.6 0.6 ** *** * 0.4 ** 0.4 Normogastria Normogastria Bradygastria p 0.2 Time effect < 0.001 0.2 Sample effect p = 0.987 Sample× Time p = 0.849 0.0 0.0 PRE 0-20 21-40 (min) PRE 0-20 21-40 (min) Time Time (mV2) (cpm) 1.2 Time effect p = 0.002 3.4 Time effect p = 0.081 Sample effect p = 0.778 Sample effect p = 0.536 1.0 Sample× Time p = 0.806 Sample× Time p = 0.383

0.8 3.2

0.6 ** 0.4 3.0

Tachygastria ** 0.2 * * Dominant Dominant frequency 0.0 2.8 PRE 0-20 21-40 (min) PRE 0-20 21-40 (min) Time Time Fig. 3. Changes in the EGG parameters during pre- and postprandial periods. The data are expressed as meansϮstandard errors. B, blank; W, water; CW, carbonated water. Time effect, sample effect, and sampleϫtime were calculated by repeated ANOVA, which was performed to assess the effect of the two experiments (W and CW). *** pϽ0.001, ** pϽ0.01, * pϽ0.05, vs. PRE (Ϫ20 min) (Dunnett’s multiple comparison test).

(bpm)

70 †† Time effect p < 0.001 B *** †† †† Sample effect p = 0.040 W 68 Sample× Time p < 0.001 *** *** CW 66 * † † † † 64 62

Heart rate 60 * * 58 * ** ** *** ** ** *** *** ***

0 PRE 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 (min) Time Fig. 4. Magnitude of changes in heart rate during pre- and postprandial periods. The data are expressed as meansϮstandard errors. B, blank; W, water; CW, carbonated water. Time effect, sample effect, and sampleϫtime were calculated by repeated †† † ANOVA, which was performed to assess the effect of the two experiments (W and CW). pϽ0.01, pϽ0.05, CWCW–B vs.

WW–B (unpaired t-test). *** pϽ0.001, ** pϽ0.01, * pϽ0.05, vs. PRE (Dunnett’s multiple comparison test). bonated water (rϭ0.516, pϭ0.024). Therefore, we per- variance in fullness at 40 min after ingestion of car- formed multiple regression analysis using the fullness bonated water, but did not reach statistical signifi cance scores as the response variable. As shown in Table 3, (pϭ0.106, pϭ0.181, respectively). a signifi cant, independent and positive correlation was DISCUSSION found between changes in heart rate and fullness at 40 min after ingestion of carbonated water (pϽ0.05). This study showed 3 major fi ndings. First, carbonated In addition, changes in heart rate tended to show a water ingestion induced a short-term but signifi cantly variance in fullness at 40 min after ingestion of water greater fullness compared to an equivalent amount of (pϭ0.055). As to EGG parameters, bradygastria ratio water. Second, similar increases in postprandial EGG and dominant frequency seemed to contribute to the powers were observed after ingestion of both water and Gastric and Cardiac Activities and Fullness after Carbonated Water 337

Table 3. Multiple regression analysis with fullness greater distention of the stomach. A possible reason was scores as the response variable. that statistical power was not suffi cient due to the small sample size. Interestingly, after water ingestion, even a Explanatory Regression Response variable p value glass of water, the peak frequency of EGG power tended variable coeffi cient to shift toward a lower band, indicating slower gastric motility as shown in our previous study (17). In con- Water Fullness at 0 min Rϭ0.59 0.089 trast, frequency shift was not noted after ingestion of ⌬HR Ϫ3.051 0.026 carbonated water despite an increase in all EGG powers. Bradygastria ratio Ϫ0.085 0.212 Further studies are needed to clarify these phenomena Dominant frequency Ϫ8.270 0.493 after carbonated water drinking using larger samples. Fullness at 40 min Rϭ0.55 0.142 The remaining question we must address is why the ⌬HR 2.110 0.055 heart rate increases after ingestion of carbonated water, Bradygastria ratio Ϫ0.257 0.730 whereas it decreases after ingestion of water. It is well Dominant frequency 7.760 0.653 known that drinking water induces sympathetic vaso- constrictor activation, but this is not accompanied by an Carbonated water increase in arterial blood pressure in healthy young sub- ϭ Fullness at 0 min R 0.44 0.345 jects (24). Relevant to this point, Routledge et al. (25) ⌬ HR 2.379 0.125 demonstrated that water ingestion in normal subjects Bradygastria ratio 0.029 0.537 caused bradycardia due to an increase in cardiac vagal Dominant frequency Ϫ4.130 0.777 activity, which may counteract the pressor effects of Fullness at 40 min Rϭ0.64 0.046 ⌬HR 2.706 0.045 sympathetic activation. Moreover, this pressor response Bradygastria ratio Ϫ0.750 0.106 to modulate blood pressure was not observed in the Dominant frequency Ϫ17.521 0.181 elderly, in transplant recipients or in autonomic failure patients, providing direct evidence for the explanation HR: heart rate. ⌬HR: postprandial HRϪpreprandial HR. of the pressor and autonomic responses to drinking Bradygastria ratio: postprandial bradygastria power/ water (25). Consistent with those previous reports, we preprandial bradygastria power. found decreased heart rates after ingestion of water as a result of normal pressor responses. Regarding carbon- ated water, we found that increases in heart rate shortly carbonated water; however, postprandial dominant fre- after ingestion may be related to the transient sympa- quency tended to shift toward a lower band, suggesting thetic acceleration via the oral gustatory receptor to acid slower gastric motility, in the water trial. Third, a signifi - taste, which also could be involved in a pain-transmis- cantly higher heart rate was found following consump- sion pathway. These stimulations induced by carbonated tion of carbonated water as opposed to water ingestion, water may be stronger at triggering sympathetic activa- and increased heart rate was a signifi cant variable con- tion than those induced by tasteless water. tributing to the variances in postprandial fullness. Regarding the association between heart rate and The classical study of Geliebter et al. (7), where 5 fullness at 40 min after ingestion of carbonated water, balloons fi lled with 0 to 800 mL of water demonstrated ⌬heart rate was a signifi cant variable contributing to that gastric distention itself triggered satiety signals, the variances in fullness. It has been reported that meal suggested that the excitation of the gastric stretch ingestion can increase postprandial heart rate (26). receptors transmitted neural signals via the vagal nerve Harthoorn and Dransfi eld (27) also demonstrated that to the hypothalamus. This suggestion was supported by both fullness and heart rate increased after lunch, and the results of an animal study (20) demonstrating that found that postprandial fullness was positively cor- gastric distention induced activation of a vagal refl ex related with heart rate, and sympatho-vagal balance mediated by stretch receptors in the proximal stomach (sympathetic predominance). Since the sympathetic in ferrets. Moreover, a clear association of gastric antral nervous system has been thought to contribute to the distention and fullness perception has been verifi ed modulation of energy homeostasis and appetite con- using labeled liquid (21), an ultrasound machine (22) trol (28), we did not assess autonomic nerve activity in and magnetic resonance imaging (23). In this study, we this study; however, the increased heart rate even after determined that 900 mL of gas was released from the 40 min could refl ect maintained sympathetic predomi- 250 mL of carbonated water by a gas pressure measure- nance and/or parasympathetic withdrawal. ment instrument. Accordingly, we suggest that short- This study has three limitations. First, there is gen- term but the greater fullness perception after ingestion der limitation. Second, the signals recorded with EGG of carbonated water was related to gastric distention correlated to some degree with gastric emptying and due to liberation of dissolved gas because carbon dioxide hence with gastric motility, but these signals may be not was the only different component between the 2 water clearly correlated to actual gastric motility; therefore, samples. the data should be interpreted carefully. Third, since full- In light of the fullness and gastric motility (electrical ness after ingestion disappeared in a short time, further responses), we failed to fi nd a relationship between car- study is needed; this should determine the consumption bonated water drinking and gastric motility in spite of of a meal after drinking, to confi rm the present results. 338 WAKISAKA S et al.

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